Neutron scattering and the glass transition in polymers – present status and future opportunities

We present results obtained by the exploration of molecular motions by neutron scattering and outline future opportunities resulting from methodological progress in high-resolution neutron spectroscopy. Starting on methododical grounds, we will commence with possible future developments in neutron spin echo spectroscopy (NSE), the prime technique for the observation of molecular processes in the nanosecond domain. After describing the scope of neutron scattering for experiments on glass-forming materials, we will present measurements of the self-correlation function, which include the β-relaxation in polyisobutylene, and address the problem of the heterogeneity of the α-process. Thereafter, we deal with different aspects of the pair correlation function, starting from coherent scattering experiments on polybutadiene, where the choice of the momentum transfer is selective for the observation of the α- or β-relaxation. Then, we emphasize results on the structural relaxation obtained for the different polymers at the first structure factor peak. Finally, by example, we will address the capability of neutron scattering, to deal with motions in polymer blends, where by judicious labeling the dynamics of the different components can be observed separately.